Heat curable silicone rubber compositions are known for their ability to resist change at elevated temperature and exposure to adverse conditions over extended periods of time. Silicone rubber compositions for use in gasketing applications require good tear and tensile strength and reduced compression set properties.
Heat cured silicone rubber compositions used in automotive gasketing applications must also have a strong resistance to hydrocarbon oils, especially at high temperatures.
Silicone rubber compositions, like most elastomeric materials, tend to shrink as a function of temperature and the thermal expansion of the material. Shrinkage is also dependent upon chemical change and the loss of volatiles during curing. Different combinations of polymers, fillers and molding temperatures are used in attempts to control the degree of shrinkage.
A cured product should have the same dimensions as its mold when both are at a curing temperature. The part, however, shrinks upon cooling. It is difficult to precisely adjust the formulation of the elastomeric material such that the optimum combination of properties and shrinkage is provided. The cost associated with manufacturing a mold which provides acceptable measured tolerances of cured parts is high. A convenient and beneficial additive to adjust shrinkage is thus desirable.
Although heat curable silicone rubber compositions having good tear strength, tensile strength and low compression set properties are known in the art, compositions for use in various automotive gasketing applications currently lack a combination of these properties along with excellent oil resistance and adjustable shrinkage. It is desirable to provide heat cured silicone elastomer compositions having the properties and durability that enable their use in various automotive gasketing applications.